1. Field of the Invention
The present invention relates to a current limit protection apparatus and a method thereof. More particularly, the present invention relates to a current limit protection apparatus having a plurality of current threshold values and a method thereof.
2. Description of Related Art
FIG. 1 is a coupling diagram of a conventional current limit protection apparatus of a computer system. Referring to FIG. 1, the reference numeral 110 represents a conventional current limit protection apparatus; the reference numeral 120 represents a connection port for connecting a universal serial bus (USB) peripheral device; and the reference numeral 130 represents a circuit connected with the current limit protection apparatus 110 in the computer system. The circuit 130 includes a USB controller 131, a resistor 132 and supply voltages VDD1 and VDD2 provided by the computer system. Moreover, GND represents a common level.
The current limit protection apparatus 110 may detect whether its output current is greater than a rated current threshold value, which is generally rated as 500 mA; if not, the current limit protection apparatus 110 normally outputs a voltage VOUT; and if yes, the current limit protection apparatus 110 stops outputting the voltage VOUT, and generates an overload warning signal for the USB controller 131 to notify the computer system that overloading occurs.
The current limit protection apparatus 110 mainly includes a metal-oxide semiconductor (MOS) transistor 111, a current detecting unit 112, a current limit control unit 113 and a driving unit 114. The current detecting unit 112 is used for detecting a conducting current of the MOS transistor 111, so as to generate a detecting result DS. The current limit control unit 113 has a preset aforementioned rated current threshold value, and the current limit control unit 113 judges whether the detecting result DS reaches the rated current threshold value. If yes, the current limit control unit 113 generates a stop driving signal TS and an overload warning signal OC. The driving unit 114 activates in response to an enable signal EN, and outputs a gate driving signal GS to turn on the MOS transistor 111 after being activated. The driving unit 114 stops outputting the gate driving signal GS when the stop driving signal TS is received.
In a conventional technique, though the computer system limits a maximum current outputted to the USB peripheral device via the current limit protection apparatus 110, however the current limit protection apparatus 110 has only one current threshold value, and when the computer system is in a sleeping mode, a power supply of the computer system may only provide a voltage of 5V and a current of 2˜2.5 A. Therefore, in this case, if the USB peripheral devices which connected with the computer system do not go into the sleeping mode sequentially, and still consume a great amount of power, the power supply will be overloaded, and the output voltage of the power supply will be decreased. Accordingly, the necessary peripheral devices of the computer system cannot work normally due to lack of basic power, and the computer system then cannot recover to a normal mode from the sleeping mode.
In a normal condition, if all of the USB peripheral devices may work in accordance with regulations, overloading of the power supply during the sleeping mode can be avoided. However, some USB peripheral devices in the market still do not comply with an USB specification in which only 2.5 mA is allowed to be consumed during the sleeping mode, which causing the computer system unable to recover to the normal mode from the sleeping mode.